Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to the prior art by inclusion in this section.
Current sensing circuits are widely used in many sensor applications to process an analog current signal and convert it to the digital domain. For current sensing applications that require high resolution and low bandwidth, a delta-sigma modulator (DSM) is often utilized to perform digitization for its superior power efficiency over other analog-to-digital converter (ADC) architectures. However, in many applications, such as sensing a current of a high impedance sensor, the current sensing circuit must have a high input impedance, so as to avoid drawing current and negatively affecting the performance of the sensor. Accordingly, when measuring a current from a high impedance sensor, conventional DSM-based current sensing circuits must utilize some kind of front-end signal-conditioning circuit, such as a pre-amp stage, to convert the high impedance sensor current signal to a low impedance output signal, so that it can be digitized.
FIG. 1 shows a conventional DSM-based current sensing system 10 for measuring and digitizing a current signal IIN from a high output impedance signal source 20. The current signal IIN is provided to a front-end signal-conditioning stage 30 before being digitized by a delta-sigma modulator 40 to provide a digital output signal DOUT. However, as the required resolution becomes higher, the high dynamic range enforced at the input nodes of both the front-end signal-conditioning stage 30 and the delta-sigma modulator 40 nevertheless results in a relatively high power implementation. Accordingly, what is needed is a current sensing circuit that provides a high input impedance, a low power consumption, and a high dynamic range.